Image scanners, also known as document scanners, convert an image on a document or photograph, or an image in a transparent medium, into an electronic form suitable for copying, storing or processing by a computer. An image scanner may be a separate device, or an image scanner may be a part of a copier, part of a facsimile machine, or part of a multipurpose device. Reflective image scanners typically have a controlled source of light, and light is reflected off the surface of a document, through an optics system, and onto an array of photosensitive devices. Transparency image scanners pass light through a transparent image, for example a photographic positive slide, through optics, and then onto an array of photosensitive devices. The optics focus at least one line, called a scanline, on the image being scanned, onto the array of photosensitive devices. The photosensitive devices convert received light intensity into an electronic signal. An analog-to-digital converter converts the electronic signal into computer readable binary numbers, with each binary number representing an intensity value.
There are two common types of image scanners. In a first type, a reduction lens system is used to focus the scanline onto the photosensor array, and the length of the photosensor array is much less than the length of the scanline. In a second type, an array of lenses is used to focus the scanline onto the photosensor array, and the length of the photosensor array is the same length as the scanline.
There is an ongoing need to reduce the cost of image scanners. There is also an ongoing need to scan surfaces larger than typical documents.